Sprint Iphone 4 goes from 5 bars to No service and Searching?

I called sprint and they tried everything on their end and told me to reset the network settings, even resetting the entire phone, and nothing helped. I read somewhere that the antenna is touchy on these phones and wearing a case may help? I would like to hear any fixes and if anyone else has had these issues. It worked completely fine the first day I had it and then it just started losing service for no reason.

Put a bumper on it